<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="./lib/jquery.js"></script>
    <style>
        .add {
            font-size: 30px;
            background-color: blue;
            color: chartreuse;
        }
    </style>
</head>

<body>
    <div class="box">你真是个天才</div>
</body>

</html>
<script>
    

function fn(){
    function fn2() {
        $(".box").on("click",function(){
            $(".box").addClass("add")
            alert("你是个人才")
        })
    }
    fn2()
}
fn()
</script>